Traction network and method for actively discharging intermediate circuit capacitor

Abstract

The invention relates to a traction network (1) of an electric vehicle, comprising a high-voltage battery (2), an inverter (6) having half-bridges (H1-H3), at least one intermediate circuit capacitor (4), at least one active discharge circuit (5) for the intermediate circuit capacitor (4), and at least one control unit (8) for actuating the active discharge circuit (5), the control unit (8) is designed to activate the active discharge circuit (5) until the high-voltage battery (2) should be accessed again or until the voltage at the intermediate circuit capacitor (4) falls below a first threshold value, and wherein at least one half-bridge (H1-H3) of the inverter (6) is subsequently switched on in order to achieve an active short circuit until the high-voltage battery (2) should be accessed again. The invention also relates to a method for actively discharging an intermediate circuit capacitor of a traction network of an electric vehicle.

Description

Technical Field

[0001] The present invention relates to a traction network and a method for actively discharging an intermediate circuit capacitor of a traction network of an electric vehicle. Background Art

[0002] In certain cases, in order to ensure contact protection, the intermediate circuit capacitor must be actively discharged relatively quickly, i.e., the remaining residual voltage after a preset time must be less than 60V. Such a situation is, for example, a collision, in which case the high-voltage battery is disconnected from the traction network by a contactor or other switching element, and the intermediate circuit capacitor is discharged to less than 60V through an active discharge circuit. Subsequently, the active discharge circuit is deactivated.

[0003] Different design methods of the active discharge circuit are known. One method is to connect at least one transistor in series with an ohmic resistor between the HV+ and HV- lines, where the transistor is cut off during normal operation and is turned on for active discharge, and the discharge is carried out through a current-limiting resistor. Another method is to use at least one half-bridge of an inverter as an active discharge circuit. In this case, one switching element is permanently turned on, and the other switching element is controlled in a linear or pulsed operating mode in order to limit the discharge current, where the switching element is usually a transistor.

[0004] Another active discharge circuit is known from patent documents DE 10 2020 132 571 B3 or US 2022 / 0393571A1. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a traction network and a method for actively discharging an intermediate circuit capacitor in order to improve the active discharge process and better ensure contact protection.

[0006] This technical problem is solved by the traction network according to the present invention and the method according to the present invention. Other advantageous design solutions of the present invention are derived from the description.

[0007] The traction network of an electric vehicle includes a high-voltage battery, an inverter with a half-bridge, at least one intermediate circuit capacitor, at least one active discharge circuit for the intermediate circuit capacitor, and at least one control unit for controlling the active discharge circuit. The control unit is designed to activate the active discharge circuit (for such a long time) until the high-voltage battery should be reconnected. Alternatively, the control unit is designed to activate the active discharge circuit until the voltage on the intermediate circuit capacitor is below a first threshold, whereupon at least one half-bridge of the inverter is switched on to effect an active short circuit until the high-voltage battery should be reconnected. During the active short circuit, the active discharge circuit can be deactivated or remain activated. This reliably prevents the intermediate circuit voltage from rising above 60 V again due to feedback (especially from the electric motor). This is based on the knowledge that unwanted feedback can occur. In this case, if the active discharge circuit is deactivated, the active discharge circuit must be reactivated, during which time the voltage on the intermediate circuit capacitor may rise again. This voltage rise is prevented according to the invention because the active discharge circuit itself or the active short circuit of at least one half-bridge of the inverter reliably prevents the voltage from rising. The first threshold is preferably below 60 V. The first threshold is preferably between 55 V and 30 V. The lower the first threshold is selected, the lower the peak current flowing due to the active short circuit, and thus the less the transistors of the half-bridge are loaded.

[0008] For example, the active discharge circuit has at least one switching element connected in series with an ohmic resistor, where at least one additional switching element is connected in parallel with this series circuit. In this case, first the switching element with the ohmic resistor is switched on until the first threshold is reached, whereupon the at least one additional switching element is switched on to effect an active short circuit. Here, a plurality of switching elements or transistors can also be connected in series so that the voltage withstand of the transistors does not have to be too high. Alternatively, the additional switching element can be omitted, so that the active discharge circuit consists only of a series circuit of a switching element and a resistor.

[0009] In a preferred alternative embodiment, the active discharge circuit consists of at least one half-bridge of the inverter, where the control unit is designed to control the at least one half-bridge in a linear or pulsed operating mode for active discharge until the first threshold is reached and then to switch on the at least one half-bridge to effect an active short circuit. The advantage of this embodiment is that no additional components are required, where only the software in the control unit needs to be adjusted.

[0010] In a further embodiment, the control unit is designed such that all half-bridges of the inverter are switched on to effect an active short circuit, thereby diverting the continuous current. It may also be provided here that all half-bridges are controlled in a linear or pulsed operating mode in order to reach a first threshold. In addition, these half-bridges can be alternately controlled for pulsed or linear operating mode and active short circuit. Thereby, the load is also evenly distributed over all half-bridges. It may also be provided here that the method is carried out with one half-bridge, which is stored, and that subsequently, when the method is to be carried out again, a different half-bridge is selected in order to thereby balance the load on these half-bridges.

[0011] In a further embodiment, the at least one half-bridge is equipped with temperature and / or current sensors and / or overcurrent / short-circuit recognition means (such as desaturation protection, abbreviated DESAT), where the control unit is designed to switch off or operate the half-bridge in a linear or pulsed operating mode when a threshold for the temperature and / or current and / or voltage on the switching element is exceeded. Thereby, damage to the half-bridge is prevented, where temperature and / or current sensors and / or overcurrent / short-circuit recognition means are already present in most inverters, so that no additional components are likewise required. Here, only the threshold for the current or voltage needs to be adjusted, since the threshold for the continuous current during an active short circuit must be chosen to be less than the current during normal operation, in which the half-bridge is controlled in a pulsed excitation manner. For example, the threshold for the current is 100 A. It may also be provided here that if a half-bridge is switched off due to temperature, the other half-bridges are switched to active short circuit, so that the previously activated half-bridge can be cooled. It may also be provided here that if initially only one half-bridge is in active short circuit and the threshold for the current is reached, one or two other half-bridges are switched on in order to divert the current.

[0012] Method for actively discharging an intermediate circuit capacitor of a traction network of an electric vehicle, where the traction network has a high-voltage battery, an inverter with half-bridges, at least one intermediate circuit capacitor, at least one active discharge circuit for the intermediate circuit capacitor, and at least one control unit for controlling the active discharge circuit, the method comprising the following steps:

[0013] a) The control unit receives a signal that the intermediate circuit capacitor is to be discharged;

[0014] b1) The control unit controls the active discharge circuit, where the control remains active until the high-voltage battery is to be reconnected, or

[0015] b2) The active discharge circuit is controlled until the voltage on the intermediate circuit capacitor is below a first threshold, where subsequently the active discharge circuit is deactivated and at least one half-bridge of the inverter is switched on to effect an active short circuit until the high-voltage battery is to be reconnected.

[0016] Regarding other design solutions according to the method, they are completely referred to the foregoing embodiments in terms of content. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be described in more detail below according to the preferred embodiments. In the drawings:

[0018] Figure 1 A schematic block diagram showing a first embodiment of a traction network;

[0019] Figure 2 A schematic block diagram showing a second embodiment of a traction network;

[0020] Figure 3 A schematic flow chart showing a method for actively discharging an intermediate circuit capacitor. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] In Figure 1 a first embodiment of the traction network 1 is shown very schematically. The traction network 1 has a high-voltage battery 2, which is connected to the rest of the traction network 1 via a contactor 3. The traction network 1 also has at least one intermediate circuit capacitor 4. Here, the intermediate circuit capacitor 4 can also consist of a series circuit of two capacitors. An active discharge circuit 5 is arranged in parallel with respect to the intermediate circuit capacitor 4. The active discharge circuit 5 has a first branch, which consists of a series circuit of a switching element in the form of a transistor T1 and an ohmic resistor R. In the second branch, a series circuit of two second transistors T2, T3 is arranged. Both branches are connected in parallel with the intermediate circuit capacitor 4. In addition, the traction network 1 has an inverter 6 with three half-bridges H1 - H3, wherein two switching elements S1 - S6 are schematically shown in each half-bridge H1 - H3, and these switching elements are generally designed as transistors. However, an embodiment using four switching elements for each half-bridge H1 - H3 is also feasible, so that for example 3L operation can be achieved. However, structural forms with different numbers of half-bridges (such as six) are also feasible. In this case, the center tap of the half-bridges H1 - H3 is connected to a motor not shown. Finally, the traction network 1 also has a voltage measuring device 7 and a control unit 8.

[0022] For example, in the event of a collision, the control unit 8 receives an instruction to actively discharge the intermediate circuit capacitor 4, where the control unit 8 or another controller additionally opens the contactor 3. The control unit 8 also receives the measured values of the voltage measuring device 7. Subsequently, in a first step, the transistor T1 is turned on, while the other transistors T2, T3 remain off. In this case, the intermediate circuit capacitor 4 is discharged through the ohmic resistor R, where the ohmic resistor limits the current so that the transistor T1 is not damaged. If the voltage across the intermediate circuit capacitor 4 drops below a first threshold (e.g., 50 V), then the two other transistors T2, T3 are turned on, so that an active short circuit exists and the intermediate circuit capacitor 4 is quickly fully discharged. During this process, the transistor T1 can remain on or can also be turned off. Here, the first threshold is selected such that the short-circuit current flowing in this case is not so large as to damage the two transistors T2, T3. If during the discharge a feedback occurs that recharges the intermediate circuit capacitor 4 (e.g., from the motor), then the voltage is immediately reduced again. If the high-voltage battery 2 should subsequently be reconnected, the control unit 8 deactivates the active discharge circuit 5 and turns off all the transistors T1 - T3. The contactor 3 is closed, where the intermediate circuit capacitor 4 is precharged beforehand through a precharge circuit (not shown).

[0023] In an alternative embodiment, the two transistors T2, T3 can be omitted, where, in this case, after reaching the first threshold, at least one of the half-bridges H1 - H3 is switched to an active short circuit (e.g., S1, S2 permanently closed).

[0024] In Figure 2An alternative embodiment of the traction network 1 is shown, in which the active discharge circuit 5 is fully integrated in the inverter 6. The current sensor 9 and the temperature sensor 10 are also additionally shown here. As a supplement or alternative to the current sensor 9, a total current sensor can also be used, which detects the DC current flowing into the inverter. Here, the measured values are also input into the control unit 8. If the intermediate circuit capacitor 4 is to be actively discharged again, the contactor 3 is opened again. In addition, at least one of the half-bridges H1 - H3 is controlled in a pulsed or linear operating mode. For example, the switching element S2 is permanently closed, and the switching element S1 is controlled to be pulsed-off or switched-on (slowly from off to on in the linear operating mode), so that the flowing current does not damage the switching elements S1, S2. This is carried out until the voltage on the intermediate circuit capacitor 4 has reached a first threshold. Subsequently, this half-bridge or all of the half-bridges H1 - H3 are switched to active short-circuit (all switching elements S1 - S6 are permanently closed). This also effectively resists the voltage increase formed on the intermediate circuit capacitor 4 due to feedback. In this case, the current and temperature sensors 9, 10 that are usually already installed in the inverter 6 can be used for monitoring to ensure that the switching elements S1 - S6 are not overloaded. For this purpose, only a slight modification to the software in the gate driver module is required. For example, the overcurrent threshold must be reduced because, unlike pulsed inverter operation, there is a continuous current flowing in the case of active short-circuit.

[0025] It should be noted here that if the voltage supply of the control unit 8 (including the gate driver) is carried out by the high-voltage side via a DC / DC converter, when the voltage on the intermediate circuit capacitor 4 drops from a specific voltage level (for example, when the voltage is less than 20 V), the high-voltage side can no longer supply the control unit 8, so the control unit 8 shuts down. If feedback occurs, the voltage rises again and the control unit 8 is restarted, so that active discharge can be carried out again.

[0026] To solve this problem, the voltage supply of the control unit 8 can also be borne by the vehicle network battery.

[0027] In Figure 3 is shown for according to Figure 2Flowchart of the active discharge method according to the embodiment. In the first step ST1, the control unit 8 obtains an active discharge request. In the second step ST2, at least one of the half-bridges H1 - H3 is operated in a pulsed or linear operating mode. In the third step ST3, it is checked whether the voltage on the intermediate circuit capacitor 4 is less than a first threshold. If not, step ST2 is continued. Conversely, if so, in the fourth step ST4, one or all of the half-bridges H1 - H3 are switched to active short circuit, and in the fifth step ST5, the overcurrent value for the gate driver is adjusted (for example, reduced to 100 A). Here, the fifth step ST5 can also be executed simultaneously with the fourth step ST4 or before the fourth step ST4. Subsequently, in the sixth step ST6, the active short circuit is maintained. Subsequently, in step ST7, it is queried whether there is a requirement to reconnect to the high-voltage battery 2. If not, the active short circuit (ST6) is maintained. Otherwise, the active short circuit is terminated (step ST8), and the overcurrent value is increased again to the value for pulsed inverter operation (step ST9).

[0028] List of reference numerals

[0029] 1 Traction network

[0030] 2 High-voltage battery

[0031] 3 Contactor

[0032] 4 Intermediate circuit capacitor

[0033] 5 Discharge circuit

[0034] 6 Inverter

[0035] 7 Voltage measuring device

[0036] 8 Control unit

[0037] 9 Current sensor

[0038] 10 Temperature sensor

[0039] H1 - H3 Half-bridges

[0040] S1 - S6 Switching elements

[0041] T1 - T3 Transistors

[0042] R Resistor

[0043] ST1 - ST6 Steps

Claims

1. A traction network (1) of an electric vehicle, comprising a high-voltage battery (2), an inverter (6) with a half-bridge (H1-H3), at least one intermediate circuit capacitor (4), at least one active discharge circuit (5) for the intermediate circuit capacitor (4) and at least one control unit (8) for controlling the active discharge circuit (5), It is characterized in that The control unit (8) is designed to activate the active discharge circuit (5) until the high-voltage battery (2) is to be connected again or until the voltage on the intermediate circuit capacitor (4) falls below a first threshold value, wherein at least one half-bridge (H1-H3) of the inverter (6) is subsequently switched on to achieve an active short circuit until the high-voltage battery (2) is to be connected again.

2. The traction network according to claim 1, characterized in that: The active discharge circuit (5) is formed by at least one half-bridge (H1-H3) of an inverter (6), wherein the control unit (8) is designed to control the at least one half-bridge (H1-H3) in a linear or pulsed operating mode to achieve active discharge until a first threshold is reached and then switch on the at least one half-bridge (H1-H3) to achieve active short circuit.

3. Traction network according to any one of the preceding claims, characterized in that The control unit (8) is designed so that all half-bridges (H1-H3) of the inverter (6) are switched on in order to achieve an active short circuit.

4. Traction network according to any of the preceding claims, characterized in that At least one half-bridge (H1-H3) is equipped with a temperature and / or current sensor (9, 10) and / or an overcurrent / short-circuit detection device, wherein the control unit (8) is designed to cut off or operate the half-bridge (H1-H3) in a linear or pulsed operating mode when threshold values ​​for the temperature and / or current and / or voltage on the switching elements (S1-S6) are exceeded.

5. A method for actively discharging an intermediate circuit capacitor (4) of a traction network (1) of an electric vehicle, wherein: A traction network (1) having a high-voltage battery (2), an inverter (6) with a half-bridge (H1-H3), at least one intermediate circuit capacitor (4) and at least one control unit (8) for controlling an active discharge circuit, the method comprising the following steps: a) receiving a signal from a control unit (8) that the intermediate circuit capacitor (4) should be discharged; b1) the active discharge circuit (5) is activated by the control unit (8), wherein the activation remains active until the high-voltage battery (2) is to be connected again, or b2) controlling the active discharge circuit (5) until the voltage on the intermediate circuit capacitor (4) falls below a first threshold value, wherein the active discharge circuit is then deactivated and at least one half-bridge (H1-H3) of the inverter (6) is switched on to achieve an active short circuit until the high-voltage battery (2) is to be connected again.

6. The method according to claim 5, characterized in that The active discharge circuit (5) is formed by at least one half-bridge (H1-H3) of an inverter (6), wherein a control unit (8) controls the at least one half-bridge (H1-H3) in a linear or pulsed operating mode in order to achieve active discharge until a first threshold is reached and then switches the half-bridge (H1-H3) to an active short circuit.

7. The method according to claim 5 or 6, characterized in that: All half-bridges (H1-H3) of the inverter (6) are switched on to achieve an active short circuit.

8. The method according to any one of claims 5 to 7, characterized in that At least one half-bridge (H1-H3) is equipped with a temperature and / or current sensor (9, 10) and / or an overcurrent / short-circuit detection device, wherein when threshold values ​​for temperature and / or current and / or voltage are exceeded, a control unit (8) switches off or operates the half-bridge (H1-H3) in a linear or pulsed operating mode.

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